Dry etching gas composition comprising sulfur-containing fluorocarbon compound having unsaturated bond and dry etching method using the same

ABSTRACT

Provided is a novel etching gas composition that comprises a sulfur-containing unsaturated compound and that is useful for etching a stacked structure of silicon-based films. A dry etching gas composition comprises a sulfur-containing fluorocarbon compound that has an unsaturated bond and that is represented by general formula (1) of CxFySz where x, y, and z are 2≤x≤5, y≤2x, and 1≤z≤2.

TECHNICAL FIELD

The present invention relates to a dry etching gas compositioncomprising a sulfur-containing fluorocarbon compound and to a dryetching method using the composition.

BACKGROUND ART

Along with the shift towards miniaturization and 3D configurations ofsemiconductor devices, the needs for an etching process have becomeincreasingly demanding year after year. Particularly in collectiveetching of a stacked SiO₂ and polysilicon (poly-Si) structure,collective etching of a stacked SiO₂ and SiN structure, or SiO₂ etchingtypical for the application to memories, etching characteristics, suchas high-speed etching for improved throughput, high selectivity overmasks, and satisfactory processed shapes (suppressed necking and bowing,vertical shapes, and so forth) are needed.

Concerning a dry etching gas composition comprising a sulfur-containingfluorocarbon compound having an unsaturated bond, Patent Literature(PTL) 1 describes a dry etching method using a sulfur-containingunsaturated compound (perfluoropropylene sulfide (C₃F₆S)). However, PTL1 relates to the application characterized by the ratio of silicon oxideto silicon nitride removed through etching (application to SiO₂/SiNselective etching) and does not describe the application characterizedby selective etching of silicon oxide and silicon nitride over anamorphous carbon layer (ACL) or the application characterized byselective etching of silicon oxide and polycrystalline silicon over anamorphous carbon layer (ACL). PTL 2 describes a dry etching method usingspecific sulfur-containing compounds, but all the sulfur-containingcompounds are saturated compounds.

CITATION LIST Patent Literature

PTL 1: Korean Patent No. 10-0574923 (Korean Unexamined Publication No.10-2001-0010568)

PTL 2: WO 2015/035381

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a novel etching gascomposition that comprises a sulfur-containing unsaturated compound andthat is useful for the application to the etching of a silicon-basedfilm stacked structure.

Solution to Problem

According to the present invention, the following are provided.

[1] A dry etching gas composition comprising a sulfur-containingfluorocarbon compound that has an unsaturated bond and that isrepresented by general formula (1) of C_(x)F_(y)S_(z) where x, y, and zare 2≤x≤5, y≤2x, and 1≤z≤2.

[2] The dry etching gas composition according to [1], where thesulfur-containing fluorocarbon compound is at least one selected from2,2,3,4,5,5-hexafluoro-2,5-dihydrothiophene (C₄F₆S) and trifluorovinyltrifluoromethyl thioether (C₃F₆S).

[3] The dry etching gas composition according to [1] or [2], comprisingthe sulfur-containing fluorocarbon compound in an amount of 1 to 100 vol%.

[4] The dry etching gas composition according to any one of [1] to [3],further comprising, in addition to the sulfur-containing fluorocarboncompound, at least one oxygen-containing compound selected from thegroup consisting of O₂, O₃, CO, CO₂, NO, NO₂, SO₂, and SO₃.

[5] The dry etching gas composition according to any one of [1] to [4],further comprising, in addition to the sulfur-containing fluorocarboncompound, at least one inert gas selected from the group consisting ofN₂, He, Ar, Ne, and Xe.

[6] A dry etching method comprising etching a silicon-containing depositor film by plasma etching using the dry etching gas compositionaccording to any one of [1] to [5].

[7] The dry etching method according to [6], where thesilicon-containing deposit or film is a deposit or film furthercontaining oxygen and/or nitrogen.

[8] The dry etching method according to [6] or [7], comprisingselectively etching the silicon-containing deposit or film over a maskmaterial.

[9] A dry etching method comprising plasma etching, by using the dryetching gas composition according to any one of [1] to [5], a stackedstructure of: (a1) carbon-containing silicon-based film, (a2) a singlecrystal silicon film, (a3) an amorphous silicon film, (a4) apolycrystalline silicon film (polysilicon film), (a5) a siliconoxynitride film, (a6) an amorphous carbon film, and/or (a7) aphotoresist film; and (b1) a silicon oxide film and/or (b2) a siliconnitride film, thereby selectively etching (b1) the silicon oxide filmand/or (b2) the silicon nitride film of the stacked structure.

[10] The dry etching method according to [9], where the stackedstructure contains (b1) the silicon oxide film and (b2) the siliconnitride film; and the method selectively etches (b1) the silicon oxidefilm over (b2) the silicon nitride film.

[11] A dry etching method comprising plasma etching, by using the dryetching gas composition according to any one of [1] to [5], a stackedstructure of: (a1) carbon-containing silicon-based film, (a2) a singlecrystal silicon film, (a3) an amorphous silicon film, (a4) a siliconnitride film, (a5) a silicon oxynitride film, (a6) an amorphous carbonfilm, and/or (a7) a photoresist film; and (b1) a silicon oxide filmand/or (b2) a polycrystalline silicon film (polysilicon film), therebyselectively etching (b1) the silicon oxide film and/or (b2) thepolycrystalline silicon film (polysilicon film) of the stackedstructure.

[12] The dry etching method according to any one of [6] to [11], whereetching is performed by generating a plasma of the etching gascomposition according to any one of [1] to [5] to form S-containing ionsor active species.

[13] The dry etching method according to any one of [6] to [11], whereetching by the dry etching gas composition according to any one of [1]to [5] is performed under plasma conditions that enable simultaneousetching of (b1) a silicon oxide film and (b2) a silicon nitride film.

Advantageous Effects of Invention

The present invention provides an etching gas composition having a highratio of a material containing silicon oxide and silicon nitride to anamorphous carbon layer (ACL) that are removed through etching.Accordingly, by using the etching gas composition of the presentinvention, a method of accurately etching a material containing siliconoxide and silicon nitride using an amorphous carbon layer as a mask isprovided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the results of etching test (1).

FIG. 2 is a bar graph showing the results of etching test (1) relativeto the etching rate of ACL.

FIG. 3 shows the results of a deposit film evaluation test.

FIG. 4 shows the composition of each deposit film formed in the depositfilm evaluation test.

FIG. 5 shows the results of etching test (2).

FIG. 6 is a bar graph showing the results of etching test (2) relativeto the etching rate of ACL.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a dry etching gas composition and a dry etching methodusing the composition in the present invention will be described indetail. The scope of the present invention, however, is not limited tothe scope described hereinafter and may be modified without departingfrom the spirit of the present invention.

The dry etching gas composition in the present invention encompasses amixed gas of a sulfur-containing fluorocarbon compound that has anunsaturated bond and that is represented by general formula (1) below ora single-component gas thereof:C_(x)F_(y)S_(z)  General formula (1):

where x, y, and z are 2≤x≤5, y≤2x and 1≤z≤2.

In view of easy handling of a dry etching gas, it is preferable to usecompounds satisfying x=2 to 4, y=4 to 8, and Z=1 in general formula (1).Exemplary suitable compounds include the following.

-   -   2,2,3,4,5,5-Hexafluoro-2,5-dihydrothiophene (C₄F₆S)

-   -   Trifluorovinyl trifluoromethyl thioether (C₃F₆S)

-   -   1,1,2,3,4,5-Hexafluoro-1,1-dihydrothiophene (C₄F₆S)

-   -   2,3-Bis(trifluoromethyl)thiirene (C₄F₆S)

-   -   3,3,3-Trifluoro-2-(trifluoromethyl)-1-propene-1-thione (C₄F₆S)

-   -   2,2,3,3,4,5-Hexafluoro-2,3,-dihydrothiophene (C₄F₆S)

-   -   2,2,3,4,4-Pentafluoro-3-butenethioyl fluoride (C₄F₆S)

-   -   2,2,3,3,3-Pentafluoropropanethioyl fluoride (C₃F₆S)

-   -   1,1,1,3,3,3-Hexafluoro-2-propanethione (C₃F₆S)

-   -   1,3,3,3-Tetrafluoro-2-(trifluoromethyl)-1-propene-1-sulfenyl        fluoride (C₄F₈S)

-   -   1,1,1,3,3,4,4,4-Octafluoro-2-butanethione (C₄F₈S)

-   -   2,3,4,5-Tetrafluorothiophene (C₄F₄S)

In the dry etching gas composition in the present invention, asulfur-containing fluorocarbon compound represented by general formula(1) having a purity of 95.0 vol % to 100.0 vol % is preferably used. Asulfur-containing fluorocarbon compound having a purity of 99 vol % ormore is more preferably used, and a sulfur-containing fluorocarboncompound having a purity of 99.9 vol % or more is further preferablyused. Examples of impurity components contained include N₂, O₂, CO₂,H₂O, HF, HCl, SO₂, and CH₄. Among these impurity components, H₂O, HF,HCl, SO₂, and the like are highly likely to corrode distributionchannels for gases and thus preferably removed as much as possiblethrough purification.

By using a sulfur-containing fluorocarbon compound represented bygeneral formula (1) mixed with another fluorocarbon (FC) gas or ahydrofluorocarbon (HFC) gas, the dry etching gas composition in thepresent invention can further enhance the selectivity of an etchingtarget material over materials excluding the etching target material ascompared with the case without incorporating a compound represented bygeneral formula (1). Moreover, in the case of etching a structurepatterned with a material excluding the etching target material,accuracy in vertical processing is also improved.

When an etching target material is an oxygen-containing Si-basedmaterial, such as SiO₂, in a structure patterned with a materialexcluding the etching target material as mentioned above, it ispreferable to use a compound represented by general formula (1) mixedwith an etching gas, such as CF₄, CHF₃, C₂F₆, C₃F₈, C₄F₈, C₄F₆, or C₅F₈,in view of selective etching and etching with satisfactory accuracy invertical processing. In particular, when a high selectivity is needed,it is preferable to mix with C₄F₈, C₄F₆, or C₅F₈ having a high C number.

When an etching target material is a nitrogen-containing Si-basedmaterial, such as SiN, in a structure patterned with a materialexcluding the etching target material, it is preferable to use, forplasma etching, a gas compound represented by general formula (1) mixedwith a HFC gas, such as CHF₃, CH₂F₂, or CH₃F, in view of selectiveetching and etching with satisfactory accuracy in vertical processing.In particular, when a high selectivity is needed, it is also effectiveto use a HFC gas having a C number of 2 or more.

By adding at least one oxygen-containing compound selected from thegroup consisting of O₂, O₃, CO, CO₂, NO, NO₂, SO₂, and SO₃ to acomposition containing a compound represented by general formula (1),the dry etching gas composition in the present invention can obtain theeffects of suppressing excessive deposition (deposits), increasing theetching rate of an etching target, and enhancing the selectivity of theetching target over materials excluding the etching target.

In the dry etching gas composition in the present invention, at leastone inert gas selected from the group consisting of N₂, He, Ar, Ne, andXe may be added to the composition containing a compound represented bygeneral formula (1). Among these inert gases, He, Ar, or Xe ispreferably used.

Exemplary etching gas compositions used in the method of the presentinvention include the following.

(a) The method can be carried out using a compound represented bygeneral formula (1) having a purity of 90 vol % or more, and the methodis preferably carried out using the compound having a purity of 99 vol %or more and is particularly preferably carried out using the compoundhaving a purity of 99.999 vol % or more.

(b) A dry etching composition used for etching preferably contains 1 to100 vol % of a compound represented by general formula (1).

(c) A dry etching composition used for etching preferably contains, inaddition to a compound represented by general formula (1), at least oneselected from the oxygen atom-containing compound group consisting ofO₂, O₃, CO, CO₂, NO, NO₂, SO₂, and SO₃. In particular, O₂ is preferablyused. The proportion of the oxygen atom-containing compound ispreferably 5 to 80% and particularly preferably 10 to 65% relative tothe total amount of the compound represented by general formula (1) andthe oxygen atom-containing compound.

(d) A dry etching composition used for etching preferably contains, inaddition to a compound represented by general formula (1) as well as inaddition to or in place of the above-mentioned oxygen atom-containingcompound group, at least one selected from the inert gas groupconsisting of rare gases and N₂. In particular, Ar is preferably used.The proportion of an inert gas contained in the etching gas compositionis preferably 1 to 80 vol % and particularly preferably 50 to 75 vol %.

As a dry etching apparatus used for dry etching in the presentinvention, any apparatus used in the technical field concerned can beused without particular limitation. For example, an apparatus of heliconwave mode, high frequency induction mode, parallel plate configurationmode, magnetron mode, microwave mode, or the like is usable.

The dry etching method in the present invention is for verticalprocessing of a fine pattern wafer of a Si-based material. Accordingly,the etching apparatus needs to be an apparatus suitable for ion-assistedetching and equipped with a vacuum chamber that can reproduce low gaspressure conditions. Under low pressure conditions, particles in aplasma tend to travel in straight line and ions for irradiating asubstrate reach the substrate without being blocked by other particles.Consequently, such low pressure conditions are advantageous for verticalprocessing since ions incident normal to the substrate increase. In thedry etching method in the present invention, the pressure inside thevacuum chamber during etching is preferably adjusted to 100 Torr to 0.1mTorr and further preferably adjusted to 100 mTorr to 0.1 mTorr.

In the dry etching method in the present invention, a compoundrepresented by general formula (1) is preferably introduced as a gasinto a vacuum chamber of an etching apparatus. For this reason, anetching apparatus used for the dry etching method in the presentinvention preferably includes a mechanism for introducing the compoundrepresented by general formula (1) as a gas and further for adjustingthe amount introduced. Moreover, regarding such a mechanism, since aplurality of gas compounds including a gas compound represented bygeneral formula (1) and other gas compounds described above, such as O₂and Ar, are effectively used depending on the purposes in the plasmaetching method in the present invention, it is preferable to includefour or more mechanisms for introducing gases and for adjusting theamounts introduced.

EXAMPLES

The present working examples (etching tests (1) and (2), deposit filmevaluation test) used, as a plasma etching apparatus, a capacitivelycoupled plasma etching apparatus of parallel plate configuration fromSAMCO Inc. The composition of a deposit film was determined by anSEM-EDX (scanning electron microscope/energy dispersive X-rayspectroscopy).

As a silicon oxide film (SiO_(m); m is a natural number), a SiO₂ filmdeposited at a thickness of 1000 nm on a silicon wafer by plasma CVD wasused. As a silicon nitride film (SiN), a SiN film deposited at athickness of 300 nm on a silicon wafer by thermal CVD was used. As anamorphous carbon film (ACL), ACL deposited at a thickness of 400 nm on asilicon wafer by plasma CVD was used.

The flow rate of a gas was expressed in sccm (standard cc/min) understandard conditions of a temperature (0° C.) and a pressure (1 atm).

The sample film thickness during etching was measured using aninterference-mode film thickness meter. The etching conditions are shownin Tables 1 and 3 below. The etching rate of a gas was calculatedaccording to the following formula.

$\begin{matrix}{{{Etching}\mspace{14mu}{rate}\mspace{14mu}\left( {{nm}\text{/}\min} \right)} = \frac{\begin{matrix}{{{sample}\mspace{14mu}{film}\mspace{14mu}{thickness}\mspace{14mu}{before}\mspace{14mu}{etching}\mspace{14mu}({nm})} -} \\{{sample}\mspace{14mu}{film}\mspace{14mu}{thickness}\mspace{14mu}{after}\mspace{14mu}{etching}\mspace{14mu}({nm})}\end{matrix}}{{etching}\mspace{14mu}{time}\mspace{14mu}\left( \min \right)}} & \left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

The A/B selectivity was calculated according to the following formula.A/B selectivity=etching rate of A film(nm/min)÷etching rate of Bfilm(nm/min)

A deposition film (hereinafter, referred to as “deposit film”) wasformed on a bare silicon wafer. The deposit film thickness was measuredby a scanning electron microscope. The conditions for forming a depositfilm and for sputtering are shown in Table 2 below. The forming rate ofa deposit film and the sputtering rate were calculated according to thefollowing formulae.

$\begin{matrix}{{{Deposition}\mspace{14mu}{rate}\mspace{14mu}\left( {{nm}\text{/}\min} \right)} = \frac{{deposit}\mspace{14mu}{film}\mspace{14mu}{thickness}\mspace{14mu}({nm})}{{deposition}\mspace{14mu}{time}\mspace{14mu}\left( \min \right)}} & \left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack \\{{{sputtering}\mspace{20mu}{rate}\mspace{14mu}\left( {{nm}\text{/}\min} \right)} = \frac{\begin{matrix}{{{deposit}\mspace{14mu}{film}\mspace{14mu}{thickness}\mspace{14mu}{of}\mspace{14mu}{unsputtered}\mspace{14mu}{sample}\mspace{14mu}({nm})} -} \\{{deposit}\mspace{14mu}{film}\mspace{14mu}{thickness}\mspace{14mu}{of}\mspace{14mu}{sputtered}\mspace{14mu}{sample}\mspace{14mu}({nm})}\end{matrix}}{{sputtering}\mspace{14mu}{time}\mspace{14mu}\left( \min \right)}} & \left\lbrack {{Math}.\mspace{14mu} 3} \right\rbrack\end{matrix}$

[Etching Test (1)]

An etching test was performed under conditions shown in Table 1 forthree samples in which SiO₂, SiN, or ACL had been deposited on eachsilicon wafer. For etching gases, perfluorocyclobutene(1,2,3,3,4,4-hexafluoro-1-cyclobutene (C₄F₆)) as a sulfur-freeComparative Example and 2,2,3,4,5,5-hexafluoro-2,5-dihydrothiophene(C₄F₆S) as a sulfur-containing Example of the present invention wereused.

TABLE 1 Etching Test Conditions (apparatus: SAMCO RIE-10NR) SAMCORIE-10NR Total gas flow rate 80 [sccm] Ar/etching gas/O₂ 40/x/y [sccm]Pressure 3.0 [Pa] RF power 300 [W]

The test results are shown in FIG. 1 . Ar was allowed to flow constantlyat 40 sccm (50%) while varying the rate of an etching gas and the rateof oxygen (O₂). When the rate of an etching gas is 20 sccm and the rateof oxygen is 20 sccm, the O₂ ratio in the graphs of FIG. 1 is 50%. Themeasurement was started from this component ratio, and the concentrationof oxygen in an etching gas composition was increased to the O₂ ratio of65% in the graphs of FIG. 1 at which the rate of an etching gas is 14sccm and the rate of oxygen is 26 sccm.

Since ACL comprises carbon, the etching rate increased with the increasein O₂ concentration in both the Example and the Comparative Example.Meanwhile, it was found that in the case of the etching gas (C₄F₆S) ofthe Example, the etching rate of SiO₂ sharply increased with theincrease in O₂ ratio to reach the maximum (approximately 70 nm/min) atthe O₂ ratio of 55% (etching gas rate of 18 sccm, oxygen rate of 22sccm), whereas the etching rate increased gradually with the increase inO₂ ratio to reach almost the maximum (approximately 70 nm/min) at the O₂ratio of 65% (etching gas rate of 14 sccm, oxygen rate of 26 sccm) inthe Comparative Example. Moreover, it was also found that in the case ofthe etching gas (C₄F₆S) of the Example, the etching rate of SiNincreased gradually with the increase in O₂ ratio to reach almost themaximum (approximately 55 nm/min) at the O₂ ratio of 65%, whereas theetching rate of SiN increased further gradually with the increase in O₂ratio to reach less than 40 nm/min even at the O₂ ratio of 65% in theComparative Example.

Regarding the results obtained in the Example and the ComparativeExample, the etching rates of SiO₂ and SiN were evaluated relative tothe etching rate of ACL. The results are shown in FIG. 2 . FIG. 2reveals the following. In the Comparative Example, when the oxygenconcentration is relatively low at the O₂ ratio of 55% (etching gas rateof 18 sccm, oxygen rate of 22 sccm), only the etching rate of SiO₂ ishigh. Consequently, it is possible to selectively etch SiO₂ over SiN andACL. Meanwhile, in the Example of the present invention, when the oxygenconcentration is relatively low at the O₂ ratio of 55% (etching gas rateof 18 sccm, oxygen rate of 22 sccm), the etching rate of SiO₂ is furtherhigh and the etching rate of SiN is also high. Consequently, it ispossible to etch both SiO₂ and SiN at higher etching rates than ACL.Further, it was also found that differences in etching rate between theExample and the Comparative Example disappear when the O₂ ratio exceeds65%.

The foregoing results revealed that remarkable differences in etchingbehavior exist between the Example of the present invention, in which asulfur-containing etching gas is used, and the Comparative Example, inwhich a sulfur-free etching gas is used. Accordingly, by utilizing thenovel etching behavior of the present invention, it was found possibleto achieve both high-speed etching and high selectivity over maskmaterials. The present Example enables selective etching of SiO₂ and/orSiN over ACL with significant differences from the Comparative Example.Moreover, by using the etching gas of the present invention incombination with a conventional etching gas, it is possible to change adifference in etching rate between SiO₂ and SiN, thereby making furtheraccurate etching possible.

[Deposit Film Evaluation Test]

Etching of a target using an etching gas is in a competing relationshipwith deposition of decomposition products of the etching gas. Duringetching, such a deposit is also formed. By using perfluorocyclobutene(1,2,3,3,4,4-hexafluoro-1-cyclobutene (C₄F₆)) as a sulfur-freeComparative Example and 2,2,3,4,5,5-hexafluoro-2,5-dihydrothiophene(C₄F₆S) as a sulfur-containing Example of the present invention, adeposit of an etching gas was formed under conditions shown in Table 2below, and the ease of the removal processing of the deposit by Arsputtering was evaluated.

TABLE 2 Conditions for Deposit Film Evaluation Test (apparatus: SAMCORIE-200NL) SAMCO RIE-200NL Deposition rate Sputtering rate Ar/etchinggas 10/20 [sccm] 50/0 [sccm] Pressure 5.0 [Pa] 5.0 [Pa] RF power 100 [W]100 [W] Time 120 [sec] 30 [sec]

The results of the deposit film evaluation test are shown in FIGS. 3 and4 . Both the deposition rate and the sputtering rate are lower in theExample of the present invention than in the Comparative Example.However, the lower ratio (SR/DR) of the sputtering rate (SR) to thedeposition rate (DR) in the Example of the present invention revealedeasier deposition and harder sputtering in the Example of the presentinvention. Such characteristics of the present invention are presumablyattributable to a sulfur-containing film since sulfur is detected in thecomposition of the deposit film as shown in FIG. 4 . From these testresults, the etching gas of the present invention was found capable ofetching deposited layers, such as SiO₂ and SiN, on a silicon wafer whileforming a deposit film that is hard to remove. The novel behavior of thepresent invention like this is useful, for example, for protectingsidewalls or mask materials during etching.

[Etching Test (2)]

An etching test was performed under conditions shown in Table 3 forthree samples in which SiO₂, SiN, or ACL had been deposited on eachsilicon wafer. For etching gases, perfluoropropene(1,1,2,3,3,3-hexafluoro-1-propene (C₃F₆)) as a sulfur-free ComparativeExample and trifluorovinyl trifluoromethyl thioether (C₃F₆S) as asulfur-containing Example of the present invention were used.

TABLE 3 Etching Test Conditions (2) (apparatus: SAMCO RIE-10NR) SAMCORIE-10NR Ar/etching gas/O₂ 50/20 (x)/**(y) [sccm] Pressure 10.0 [Pa] RFpower 300 [W]

The test results are shown in FIG. 5 . Ar and an etching gas wereallowed to flow constantly at rates of 50 sccm and 20 sccm,respectively, while varying the rate (sccm) of oxygen (O₂). The etchingof ACL started at around over 20% of the rate of oxygen relative to thetotal (x+y) of an etching gas (x) and oxygen (y).

In the case of the etching gas (C₃F₆S) of the Example, the etching rateof SiO₂ sharply increased with the increase in O₂ ratio to reach themaximum (approximately 70 nm/min) at the O₂ ratio of near 25%.Meanwhile, in the Comparative Example (C₃F₆), the etching rate of SiO₂hardly increased despite the increase in O₂ ratio and increased sharplyat around the O₂ ratio of over 20%. Moreover, in the case of the etchinggas (C₃F₆S) of the Example, the etching rate of SiN increased graduallywith the increase in O₂ ratio to reach almost the maximum (approximately55 nm/min) at around the O₂ ratio of over 30%. Meanwhile, in theComparative Example, the etching rate of SiN hardly increased despitethe increase in O₂ ratio and increased sharply at around the O₂ ratio ofover 20%.

Regarding the results obtained in the Example and the ComparativeExample, the etching rates of SiO₂ and SiN were evaluated relative tothe etching rate of ACL. The results are shown in FIG. 6 . FIG. 6reveals the following. In the Comparative Example, when the oxygenconcentration is relatively low at the O₂ ratio of 20% or less, all theetching rates of SiO₂, SiN, and ACL are low. Meanwhile, in the Exampleof the present invention, when the oxygen concentration is relativelylow at the O₂ ratio of 20% or less, both the etching rates of SiO₂ andSiN are extremely high. Consequently, it is possible to etch both SiO₂and SiN at higher etching rates than ACL. Moreover, it was also foundthat differences in etching rate between the Example and the ComparativeExample disappear when the O₂ ratio exceeds 30%.

From the foregoing results, it was found in etching test (2) as well inthe same manner as etching test (1) that remarkable differences inetching behavior exist between the Example of the present invention, inwhich a sulfur-containing etching gas is used, and the ComparativeExample, in which a sulfur-free etching gas is used. In other words, itwas found possible, by utilizing the novel etching behavior of thepresent invention, to achieve both high-speed etching and highselectivity over mask materials. The present Example enables selectiveetching of SiO₂ and/or SiN over ACL with significant differences fromthe Comparative Example. Moreover, by using the etching gas of thepresent invention in combination with a conventional etching gas, it ispossible to change a difference in etching rate between SiO₂ and SiN,thereby making further accurate etching possible.

The invention claimed is:
 1. A dry etching method, comprising etching asilicon-containing deposit or film by plasma etching with a dry etchinggas composition consisting of: a sulfur-containing fluorocarbon compoundthat has an unsaturated bond and that is represented by general formula(1) of CxFySz wherein x, y, and z are 2≤x≤5, y≤2x, and 1≤z≤2, andoptionally, at least one compound selected from the group consisting of:at least one oxygen-containing compound selected from the groupconsisting of O₂, O₃, CO, CO₂, NO, NO₂, SO₂, and SO₃; at least one inertgas; at least one fluorocarbon (FC); and at least one hydrofluorocarbon(HFC).
 2. The dry etching method according to claim 1, wherein thesilicon containing deposit or film is a deposit or film furthercontaining oxygen and/or nitrogen.
 3. The dry etching method accordingto claim 1, comprising selectively etching the silicon-containingdeposit or film over a mask material.
 4. The dry etching methodaccording to claim 1, wherein etching is performed by generating aplasma of the etching gas composition to form S-containing ions oractive species.
 5. The dry etching method according to claim 1, whereinthe sulfur-containing fluorocarbon compound is

2,2,3,4,5,5-Hexafluoro-2,5-dihydrothiophene

Trifluorovinyl trifluoromethyl thioether

1,1,2,3,4,5-Hexafluoro-1,1-dihydrothiophene

2,3-Bis(trifluoromethyl)thiirene

2,2,3,3,4,5-Hexafluoro-2,3,-dihydrothiophene

2,3,4,5-Tetrafluorothiophene (C₄F₄S), or mixture thereof.
 6. The dryetching method according to claim 1, wherein the at least one inert gasis selected from the group consisting of Na, He, Ar, Ne, and Xe.
 7. Thedry etching method according to claim 1, wherein the at least onefluorocarbon (FC) is selected from the group consisting of CF₄, C₂F₆,C₃F₈, C₄F₈, C₄F₆, and C₅F₈.
 8. The dry etching method according to claim1, wherein the at least one hydrofluorocarbon (HFC) is selected from thegroup consisting of CHF₃, CH₂F₂, and CH₃F.
 9. The dry etching methodaccording to claim 1, wherein the dry etching gas composition consistsof: the sulfur-containing fluorocarbon compound being

2,2,3,4,5,5-Hexafluoro-2,5-dihydrothiophene, and the at least one inertgas being Ar.
 10. The dry etching method according to claim 1, whereinthe dry etching gas composition consists of: the sulfur-containingfluorocarbon compound being

2,2,3,4,5,5-Hexafluoro-2,5-dihydrothiophene, the at least oneoxygen-containing compound being O₂; and the at least one inert gasbeing Ar.
 11. The dry etching method according to claim 1, wherein thesulfur-containing fluorocarbon compound is

3,3,3-Trifluoro-2-(trifluoromethyl)-1-propene-1-thione,

2,2,3,4,4-Pentafluoro-3-butenethioyl fluoride,

2,2,3,3,3-Pentafluoropropanethioyl fluoride,

1,1,1,3,3,3-Hexafluoro-2-propanethione,

1,1,1,3,3,4,4,4-Octafluoro-2-butanethione, or mixture thereof.
 12. Thedry etching method according to claim 1, wherein the sulfur-containingfluorocarbon compound is

1,3,3,3-Tetrafluoro-2-(trifluoromethyl)-1-propene-1-sulfenyl fluoride.13. A dry etching method, comprising plasma etching, with a dry etchinggas composition consisting of: a sulfur-containing fluorocarbon compoundthat has an unsaturated bond and that is represented by general formula(1) of CxFySz wherein x, y, and z are 2≤x≤5, y≤2x, and 1≤z≤2, andoptionally, at least one compound selected from the group consisting of:at least one oxygen-containing compound selected from the groupconsisting of O₂, O₃, CO, CO₂, NO, NO₂, SO₂, and SO₃; at least one inertgas; at least one fluorocarbon (FC); and at least one hydrofluorocarbon(HFC), a stacked structure of: (a1) carbon-containing silicon-basedfilm, (a2) a single crystal silicon film, (a3) an amorphous siliconfilm, (a4) a polycrystalline silicon film (polysilicon film), (a5) asilicon oxynitride film, (a6) an amorphous carbon film, and/or (a7) aphotoresist film; and (b1) a silicon oxide film and/or (b2) a siliconnitride film, thereby selectively etching (b1) the silicon oxide filmand/or (b2) the silicon nitride film of the stacked structure.
 14. Thedry etching method according to claim 13, wherein the stacked structurecontains (b1) the silicon oxide film and (b2) the silicon nitride film;and the method selectively etches (b1) the silicon oxide film over (b2)the silicon nitride film.
 15. The dry etching method according to claim13, wherein etching is performed by generating a plasma of the etchinggas composition to form S-containing ions or active species.
 16. The dryetching method according to claim 13, wherein etching by the dry etchinggas composition is performed under plasma conditions that enablesimultaneous etching of (b1) a silicon oxide film and (b2) a siliconnitride film.
 17. A dry etching method, comprising plasma etching, witha dry etching gas composition consisting of: a sulfur-containingfluorocarbon compound that has an unsaturated bond and that isrepresented by general formula (1) of C_(x)F_(y)S_(z) wherein x, y, andz are 2≤x≤5, y≤2x, and 1≤z≤2, and optionally, at least one compoundselected from the group consisting of: at least one oxygen-containingcompound selected from the group consisting of O₂, O₃, CO, CO₂, NO, NO₂,SO₂, and SO₃; at least one inert gas; at least one fluorocarbon (FC);and at least one hydrofluorocarbon (HFC), a stacked structure of: (a1) acarbon containing silicon-based film, (a2) a single crystal siliconfilm, (a3) an amorphous silicon film, (a4) a silicon nitride film, (a5)a silicon oxynitride film, (a6) an amorphous carbon film, and/or (a7) aphotoresist film; and (b1) a silicon oxide film and/or (b2) apolycrystalline silicon film (polysilicon film), thereby selectivelyetching (b1) the silicon oxide film and/or (b2) the polycrystallinesilicon film (polysilicon film) of the stacked structure.
 18. The dryetching method according to claim 17, wherein etching is performed bygenerating a plasma of the etching gas composition to form S-containingions or active species.